Rename [I]DropBox[Service] to [I]DropBoxManager[Service].

Un-hide the DropBoxManager interface, and update the public API accordingly.
diff --git a/cleanspec.mk b/cleanspec.mk
new file mode 100644
index 0000000..683e303
--- /dev/null
+++ b/cleanspec.mk
@@ -0,0 +1 @@
+$(call add-clean-step, rm -rf $(OUT_DIR)/target/common/obj/JAVA_LIBRARIES/framework_intermediates/src/core/java/com/android/internal/os/IDropBoxService.java)